Two material three/five layer preform

ABSTRACT

A plastic preform from which a plastic container is blow molded. The preform replaces a three layer preform by providing a preform which is of a five layer construction in the base forming portion thereof and wherein a secondary material which forms the core layer of the three layer preform construction is divided into an inner intermediate layer and an outer intermediate layer by a third injection of material. The third injected material is preferably the same material as the primary material which is first injected. This results in the reduction of the cost of the preform and also provides remaining in the injection nozzle a quantity of the last injected material which is the same as the first injected material for the following preform in the same preform injection mold cavity. &lt;IMAGE&gt;

This invention relates in general to new and useful improvements inplastic preforms from which plastic containers are blow molded, and mostparticularly to a plastic preform which is of a laminated construction.

Polyethylene terephythalate (PET) preforms and containers blow moldedfrom such preforms are well known. However, PET per se does not have allof the necessary characteristics desired for containers. Accordingly,there has been developed a laminated preform which is primarily of afive layer construction including PET inner and outer layers, inner andouter intermediate barrier layers and a core which may be formed of PETor some other plastic. Krisbnakumar et al U.S. Pat. No. 4,609,516granted Sept. 2, 1986 and Beck U.S. Pat. No. 4,550,043 granted Oct. 29,1985 are typical recent patents granted with respect to laminatedpreforms and containers blow molded therefrom.

This invention in particular relates to a plastic preform which isprimarily of a three layer construction including inner and outer PETlayers and an intermediate core layer. Such preforms are also known buthave the deficiency of the core layer material being more expensive thanPET and further being unnecessary in the base portion of the resultantblow molded container due to the lack of biaxial orientation of the baseportion and therefore a lack of reduction of thickness of the preformportion which forms the base portion of the resultant container.

This invention in particular relates to a third injection of plasticmaterial into a preform injection mold cavity to complete the preformwith this third injection of plastic material forming a core within theoriginal core material and permitting the replacement of the moreexpensive core material in the base forming portion of the preform.

Further, while suitable apparatus has been devised for the sequentialinjection of different plastic materials into a preform injection moldcavity, it is to be understood that a nozzle through which the plasticmaterial is injected into the preform injection mold cavity will haveretained therein a small portion of the last injected material. The netresult is that this retained plastic material within the nozzle becomesthe first injected material in the formation of a next preform in thesame preform injection mold cavity. It is undesirable to have the firstinjected plastic material into the preform injection mold cavity thatwhich forms the core of a three layer preform. However, by making thelast injected material the same or substantially the same as the firstinjected material, namely PET, this deficiency of the present moldingapparatus can also be overcome.

Most particularly, in accordance with this invention, there is a firstinjection of a metered amount of a primary plastic material followed bya second injection of a metered amount of a secondary plastic materialwith the secondary plastic material serving to advance a first injectedprimary material into the preform injection mold cavity with the firstinjected material being wiped along the walls of the injection moldcavity and the secondary material forming a core between inner and outerlayers of the primary material. By controlling the volumes of the twoinjected materials, particularly the secondary material, and thenfilling the preform injection mold cavity by way of a third injection,the quantity of the secondary material may be greatly reduced. Further,by making the third injected material the same as the primary material,there remains in the injection nozzle to be first introduced into thepreform injection mold cavity in the formation of the next followingpreform the same material as the primary material whereby the tip end ofa neck finish portion of a preform will be of the desired material.

With the above and other objects in view that will hereinafter appear,the nature of the invention will be more clearly understood by referenceto the following detailed description, the appended claims, and theseveral views illustrated in the accompanying drawings.

FIG. 1 is a half sectional view taken through a conventional preforminjection mold which has injected molded therein a preform of athree/five layer construction in accordance with the invention.

FIG. 2 is a diagram showing the injection sequence time of the threeinjections of plastic material into the preform mold cavity.

FIG. 3 is a half sectional view taken through a container blow moldedfrom the preform of FIG. 1 with intermediate parts of the container bodybeing broken away, the different layers not being shown.

Referring now to the drawings in detail, it will be seen that there isillustrated in FIG. 1 a conventional preform injection mold identifiedby the numeral 10. The mold 10 is preferably of a multiple cavity typehaving a plurality of cavities 12 in which there is positioned a core14. Each cavity 12 is provided with a base opening defining a seat 16for an injection nozzle 18. The opening in the base of the mold 10 alsoincludes a sprue opening 20 into the bottom of the cavity 12.

The mold 10 has associated therewith an openable neck ring 22 which isseparable in sequence first from the mold 10 in conjunction with thecore 14 to withdraw an injected preform, such as the preform 24, fromthe cavity 12 and then from the core 14 to release the molded preform24, normally after the preform 24 has been stripped from the core 14.

The illustrated preform 24 includes a neck finish portion generallyidentified by the numeral 26 and including outer threads 28, a tamperband retaining shoulder 30 formed by a ring 32, and a support or cappingflange 34.

Below the neck finish forming portion 26, the preform 24 includes ashoulder forming portion 36 which is of a tapered increasing thicknessand which is connected to the neck finish forming portion 26 by a shortring portion 38.

Below the shoulder forming portion 36 is an elongated body formingportion 40 which is substantially cylindrical except for the slighttaper of the cavity 12 and the core 14 and which is of a uniformthickness. The body forming portion 40 terminates in a base formingportion 42 which includes a cylindrical part 44 and a generallyhemispherical bottom part 46. At this time it is pointed out that thecylindrical part 44 increases in thickness as compared to the bodyforming portion 40.

The preform 24 is formed generally in accordance with the Pocock et alU.S. Pat. No. 4,525,401 granted June 25, 1985 wherein the base formingportion is of a greater wall thickness so as to permit a reduction inthickness of the intermediate or core forming layer.

As is best shown in FIG. 2, the preform 24 is formed by the sequentialinjection of molten plastic material into the cavity 12. A preselectedmetered amount of a primary material A is first injected into the bottomportion of the cavity 12 through the nozzle 18. Next, a preselectedmetered amount of a secondary material B is injected into the cavity 12with the material B forcing the material A into the cavity 12 with thematerial A adhering to the cavity walls as it passes into the cavity andthe material B entering into the separated layers of the material A inthe manner generally disclosed in the Krishnakumar et al and Beckpatents.

Previously, only the amount of the material A was metered, with thematerial B being injected in a quantity to completely fill the cavity12. However, in view of the fact that the material B will normally bemore expensive than the material A, it is desired to restrict the use ofthe material B, particularly in the base forming portion 42. Inaccordance with this invention, this is accomplished by a third separateinjection of molten plastic material, material C, into the mold cavity12 to complete the filling of the mold cavity 12. The material C islocated substantially entirely within the base forming portion 42 as isclearly shown in FIG. 1.

At this time it is pointed out that the injection of the material Cresults in a material saving of the material B to the extent of thequantity of the material C.

Further, it is to be noted from FIG. 1 that the last injected materialwill not only fill the screw opening 20, but also the final injectionpassage of the nozzle 18, which final injection passage is customary andnot shown. It will be thus apparent that the quantity of the material Cremaining within the final nozzle passage will be that material which isfirst injected into the cavity 12 in the formation of the next followingpreform 24. In the past, it has been found undesirable to inject alimited quantity of the material B at the beginning of the injectionmolding cycle.

In the illustrated preform 26, it will be seen that the material Bextends substantially to the top of the neck finish portion 26 althoughit may terminate lower in the neck finish portion 26, depending upon theamount of the material A which is initially injected into the cavity 12.The material B accordingly forms a core 48 separating the material Ainto an inner layer 50 and an outer layer 52. Thus, the preform 24 isprimarily of a three layer construction.

At the present state of the plastic material art, virgin PE material isthe preferred material for material A. On the other hand, depending uponthe usage of the resultant container, the material B may be selectedfrom a variety of materials including colored PET, recycled PET, MXD-6nylon; copolyesters, polypropylyene PP), PP/PET blend,polyacrylonitrile, polycarbonate, and the like.

Prior to this invention, the material A would constitute 40-60% of thevolume of the preform 24 while the material B would constitute theremainder of the volume of the preform 24 thus varying between 40 and60% of the total volume. In accordance with this invention, there can bea material saving of the material B by filling the cavity 12 with thematerial C. The percent volume of the material B can be reduced to 30-40while the percent volume of the material C will be between 10 and 20.

Referring once again to FIG. 1, it will be seen that in the base formingportion 42, the material C forms a core layer 54 within the layer 48,dividing the layer 48 into an inner intermediate layer 56 and an outerintermediate layer 58 while the inner layer 50 and the outer layer 52remains substantially the same. Thus the base forming portion 42 is of afive layer construction.

Further, as is clearly shown at the bottom of the preform 24, the lastinjected plastic material is the plastic material C which is in the formof a sprue 60 that extends through the outer intermediate layer 58 andthe outer layer 52. As stated above, the material C is preferably thesame as the material A, namely PET.

Referring now to FIG. 3, it will be seen that the preform 24 is blowmolded to form, in a conventional manner, a container 62. The container62 will have a neck finish portion 26 identical to that of the preform24. It will also include an unstretched and thus unoriented ring portioncorresponding to the ring portion 38.

On the other hand, the shoulder forming portion 36 will be graduallystretched both axially and radially to be of a decreasing thickness andincreasing biaxial orientation to define a shoulder 64.

The body forming portion 40 of the preform 24 will be both axially andradially materially stretched to form a highly biaxially orientedcontainer body 66. Finally, the base forming portion 42 of the preform24 will become an outer generally cylindrical base portion 68, asupporting curved annulus 70 and a bottom wall 72. It will be seen thatthe base of the container 62 gradually increases in thickness towardsthe center of the base with the center of the base being substantiallyunstretched and of the same thickness as the extreme bottom of thepreform 24.

From the foregoing, it will be seen that the conventional three layercontainer may be modified so that the base of such a container isessentially of a five layer construction while the body portion 66 andthe upper part of the container will be of a three layer construction.On the other hand, the great reduction of the secondary material in thecontainer base in no way detracts from the appearance, strength orpossible barrier characteristics of the resultant container. Thus, inaccordance with this invention the container 62 may be made at a lessermaterial cost than a like container which is solely of a three layerconstruction.

Although only a preferred embodiment of the preform has beenspecifically illustrated and described herein, it is to be understoodthat the preform may be varied without departing from the spirit andscope of the invention a defined by the appended claims.

We claim:
 1. An injection molded plastic perform for blow molding to form a container, said preform being in part formed in three layers and in part five layers, said preform comprising a neck finish portion, a shoulder forming portion, a body forming portion, and a base forming portion, at least said body forming portion and said base forming portion having inner and outer layers formed of a primary material and separated by a layer of a secondary material; said preform being improved in that in said base forming portion a central part of said secondary material is replaced by a core layer of material other than and less costly than said secondary material, thus producing said five layer part, said preform at least in said body forming portion being formed of only three layers with said secondary material forming a relatively thick core layer.
 2. A preform according to claim 1 wherein said preform in said base forming portion being of a five layer construction with said secondary material separated into relatively thin inner and outer intermediate layers.
 3. A preform according to claim 2 wherein said material other than said secondary material is the same as said primary material whereby said preform is of a two material construction.
 4. A preform according to claim 2 wherein said material other than said secondary material is the same as said primary material whereby said preform is of a two material construction and the material last injected into a preform injection mold cavity is the same as the material first injected into a preform injection mold cavity.
 5. A preform according to claim 1 wherein said material other than said secondarY material is the same as said primary material whereby said preform is of a two material construction.
 6. A preform according to claim 1 wherein said material other than said secondary material is the same as said primary material whereby said preform is of a two material construction and the material last injected into a preform injection mold cavity is the same as the material first injected into a preform injection mold cavity.
 7. A preform according to claim 1 wherein said primary material and said secondary materials are of preselected metered quantities and said material other than said second material is of a quantity to complete filling of a preform injection mold cavity.
 8. A preform according to claim 1 wherein said secondary material extends as a core through said shoulder forming portion into said neck finish portion.
 9. A preform according to claim 1 wherein said base forming portion includes a part forming an extension of said body forming portion and of an increased wall thickness as compared to an adjacent part of said body forming portion.
 10. A plastic container formed by blow molding a preform according to claim
 1. 